I've got the N54(twin turbo gasoline) with the similar setup of reservoir and asked my SA why BMW doesn't crimp those lines, he said it's vacuum (not positive presure) so no need for them to be crimped. well apparently sometimes they come off.

BTW, get used to this turbo setup, BMW is getting rid the I-6 NA engine and swiching to I-4 twin-turbo for x28i series on all cars on the next iteration.